The present invention relates, in general, to semiconductor devices, and more particularly, to bipolar transistors.
In the past, the semiconductor industry has utilized a variety of methods to form bipolar transistors. One problem associated with the prior methods is controlling dopant distributions within the transistor's base. Prior transistor formation methods require either emitter implant annealing, oxide sidewall formation, or other high temperature (above 900.degree. C. Celsius) operations that disturb dopant distributions within the transistor's base layer. Such methods often result in a transistor having high base leakage current that degrades the transistor's efficiency. Additionally, disturbing the dopants modifies the transistor's current gain.
In addition, the bipolar transistors formed by the prior implementation methods generally have non self-aligned emitter-base contacts. Consequently, extra space must be provided between the emitter and base contacts in order to ensure that the contacts do not overlap. The extra space increases the transistor's cost, and increases base resistance thereby degrading the transistor's performance.
Accordingly, it is desirable to have a method of forming a bipolar transistor that does not disturb base dopant profiles, that results in a transistor having low base leakage current, that provides accurate control of the transistor's current gain, and that has self-aligned emitter-base contacts.